The use of a polyol in the preparation of polyurethanes by reaction of the polyol with a polyisocyanate in the presence of a catalyst and perhaps other ingredients is well known. Aromatic polyester polyols are widely used in the manufacture of polyurethane and polyurethane-polyisocyanurate foams and resins.
Aromatic polyester polyols are attractive because they tend to be low in cost, yet can be used to produce a wide variety of cellular foams having excellent properties and adaptable for many end use applications. One class of aromatic polyester polyols used commercially is polyol products produced by esterification of phthalic acid or phthalic acid anhydride with an aliphatic polyhydric alcohol, for example, diethylene glycol. This type of polyester polyol is capable of reacting with organic isocyanates to produce, for example, coatings, adhesives, sealants, and elastomers (“CASE materials”), that can have excellent characteristics, such as tensile strength, adhesion, and abrasion resistance. Such aromatic polyester polyols may also be used in formations for production of rigid polyurethane or polyisocyanurate foam.
One problem generally encountered when using aromatic polyester polyols, with a desirable high aromatic ring content, is that they are generally characteristically high in dynamic viscosity, making handling very difficult. Often, aromatic polyester polyols must be diluted or dissolved in relatively large amounts of a suitable solvent to enable producing low viscosity, easy-to-apply coating compositions upon being mixed with a curing or crosslinking agent.
Ideally, an aromatic polyester polyol has a dynamic viscosity that is sufficiently low to allow ease of pumping and mixing without the use of solvents or other viscosity modifying additives. An aromatic polyester polyol having too great a dynamic viscosity can cause difficulties in transfer of the material, as for example from storage to reactor or from the final product to the final application of the product. Excessive dynamic viscosity also can be a serious obstacle to efficient mixing with other CASE material ingredients, such as an isocyanate.
Thus, there is a need for low viscosity aromatic polyester polyols that are economical to produce and can be converted into cellular foams and other CASE materials having excellent properties. It is further desirable to have an aromatic polyester polyol having a low viscosity and can also meet the required needs for flame retardation.